The invention relates to apparatus for guiding and steering pipe casing to form a cased bore underground by boring and pushing the casings through a bore with an earth boring machine. In particular, the invention relates to a guidance and steering apparatus in which the direction of the pipe casing is controlled in both the vertical and horizontal planes during boring.
Prior earth boring machines are known which are slidably mounted and reciprocated longitudinally along a track by means of a hydraulic piston assembly. The forward end of the boring machine rotatably mounts an auger which is rotated within the interior of the pipe casings with the forward end of the auger boring a hole in the earth. The auger bores the hole and carries the dirt outwardly for ejection at the boring machine. The hydraulic pistons which are forced on the boring machine to drive the pipe casings through the bore as it is formed. Successive pipe casings are attached to the string of pipe casings as the bore progresses. A steering head is typically located at the forward pipe casing and is provided with a directional control device. Typical earth boring machines are disclosed in U.S. Pat. Nos. 4,042,046, 4,013,134, and 4,438,820. U.S. Pat. No. 4,042,046 discloses an earth boring machine having a double jointed steering head so that its direction may be controlled in both the vertical and horizontal planes. However, the resulting mechanism is relatively complicated and unreliable because it involves considerably more moving parts which are at the end where the cutting occurs and considerable dynamic forces are imparted. The system does not have a reliable means for measuring the position of the cutting head in both the horizontal and vertical planes so that it may be steered accurately. U.S. Pat. Nos. 4,042,046 and 4,013,134 utilize a conventional water level to determine the grade of the casing. That type of device includes a sight tube on an indicator board at the boring pit station connected to a water line affixed to the top of the casing being bored and pushed through the ground. Any deviation in the leading edge of the casing from the desired grade either up or down provides a corresponding response to the water level in the sight tube at the boring pit. Based on the readings of the sight tube, the operator in the boring pit may pivot the steering head of the casing in the vertical plane by means of a mechanical linkage. However, the water line connected to the sight tube must be vented on both ends. If the device is used below the water table, water can enter the tube and interfere with the reading of the sight tube. The water level devices also have inherent vibration problems with necessitate that the apparatus be shut down to take a reading of the sight tube. The sight tube cannot be monitored simultaneously with the boring operation. With the vibrations, air locks are often created which interfere with the accuracy of the reading in the sight tube. The above inaccuracies can result in the final line being off grade which often requires re-boring. U.S. Pat. No. 4,438,820 proposes an improved rate sensor for eliminating the problems utilized in water level sensors. However, the problem remains that the prior art earth boring machines for cased bores do not recognize the ability to provide means for accurately measuring the position of the steering head in both the vertical and horizontal planes as opposed to being able to sense grade only. The result is that even if the grade of the cased bore is accurate, the cased bore has deviated in its horizontal position.
In addition to the limitations of the position sensors of the prior art earth boring and casing machines, have been the problem of suitable mechanical means for pivoting the steering head relative to the casings in two degrees of freedom so that large mechanical portions are not required. Prior boring machines have utilized circular pivot flanges, such as shown in U.S. Pat. No. 4,042,046, and mechanical actuation rods affixed to the steering head which are actuated by racks assemblies to pivot the steering head. Pivot connections of the type utilized heretofore in the prior art have required large mechanical portions to move the steering head which have prevented them from being precisely controlled by small incremental forces necessary for accurate steering.
Accordingly, an object of the present invention is to provide an improved guidance and steering apparatus for an earth boring machine which accurately controls the direction of a steering head and cased bore formed thereby in both the horizontal and vertical planes in a simple and reliable manner.
Another object of the present invention is to provide improved hinge assemblies for connecting the steering head to a forward casing of an earth boring machine so that the steering head may be simply and reliably rotated in two-degrees of freedom by small mechanical forces and precise control.
Another important object of the present invention is to provide an improved guidance system for an earth boring machine which accurately measures the position of a pipe casing during boring operations to accurately and continuously display deviations in the vertical and horizontal directions.
Another object of the present invention is to provide an improved guidance and steering system for an earth boring machine wherein deviations from vertical and horizontal positions of a pipe casing can be determined and nullified by precisely moving the steering head in two-degrees of freedom during boring.
Another object of the invention is to provide an improved hinge assembly for pivotably connecting a steering head and forward casing of an earth boring machine which includes a low friction bearing so that the steering head may be rotated about two orthogonal axes under precise mechanical control and precise steps.